I've figured out what Harry's "sense of doom" reminds me of. The old action movie Timecop with Van Damme. The antagonist there used a clever plot to help a younger version of himself succeed in the past, but they had to avoid touching because "the same matter cannot occupy the same space". In the end the protagonist forces them to touch, whereupon they both die in freaky fashion and disappear from the timeline. But it's probably just another of Eliezer's clever shout-outs, not an actual clue.